We are using Electroless Nickel/Gold Immersion on both 
     SMT and Mixed Technology Boards.  The results have been 
     fantastic on the 100% SMT boards and the only drawback 
     on the Flow-soldered boards is that the pot becomes 
     contaminated with Gold rather quickly.  We have stepped 
     up our solder samples and pot purges to overcome the 
     contamination problem.
     
     I'm not sure of the exact terminology on your question 
     #1 but I always refer to the Gold used on edge 
     connectors as "Electroless or Electroplated" maybe 
     someone else can help with the terminology.
     
     #2.)  Our in-house specification calls for 100 
     microinches of Nickel and 2-6 microinches of Gold.  Our 
     PWBs measure 4 microinches of Gold consistently.
     
     #3.)  Yes.
     
     #4.)  Our PWB vendor recommends the 2-6 microinch spec.
     I have seen other company specifications range from 2-4 
     microinches minimum.
     
     Of course another drawback on Immersion Gold is the 
     cost.  We were able to justify the increased material 
     cost on the improved yields.  We are actively seeking 
     out new PWB finishes,(OSPs, Palladium, etc.)
     
     This Months "Printed Circuit Fabrication" magazine 
     covers several PWB finishes.


______________________________ Reply Separator _________________________________
Subject: FAB: Electroless Nickel - Immersion Gold
Author:  [log in to unmask] at INTERNET
Date:    7/12/96 9:25 AM


     My company is in the process of evaluating the use of Electroless Nickel 
     - Immersion Gold as a finish, for both SMT and mixed technology PWBs.  
     Is this a good plating system to evaluate??  Is there any "conventional 
     wisdom" that we're missing?
     
     Secondly, some questions about the gold deposition.
     1. Is "electroless gold" the same as "immersion gold?" 
     2. How thick can we expect the gold to deposit?
     3. Is the gold deposition process a self limiting one?
     4. How much gold is required to adequately keep the nickel solderable?
     
     Any other comments regarding this topic is appreciated.
     
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